Vegas Pro Preview freezing

basically I am working on a video but my Vegas is been stupid, every time i add a different clip it lags as it switches to it yet when i first load sony vegas and play it from the start its fine.... only after it's played once it has this problem on the preview screen. Also media manager is OFF
To understand me more I recorded the problem

Vegas is a Video editor that likes encoded source material that conforms to video standards in the TV and Film industries. The video standard in your use case would be 1920x1080x59.94P FPS, or 3840x2160x59.94P FPS. A straight 60FPS should work too, but Media Info results similar to 58.465 to 60.366 will cause playback issues in Vegas.